During the Siege of Leningrad, St. Isaac's Cathedral (Isaakievskiy Sobor), was the tallest building and very visible from all sides of Leningrad, and remained intact and untouched. In the beginning of the war, the threat to Leningrad and its suburbs became apparent. The conversation of how to evacuate the art treasures of the palaces began to Pavlovsk, Peterhof, Pushkin, and other inland locations.
However, not all art treasures managed to get out. The question arose where to find reliable storage for all items. Options were rejected one by one, until a former artillery officer, who has offered to create storage in the basement of St. Isaac's Cathedral. The venture was risky, but there is a simple explanation for that - when shelling the city begin, the Germans would use the dome as a checking point and will try to preserve this point for further attack. His proposal was accepted. So, all 872 days of the blockade museum treasures wasn't not removed and lay in the safe place and it has never been a direct artillery fire.
And yet, the dome of St. Isaac's Cathedral was closed gray camouflage fabric during the siege. With reference was lost for plane, and the probability of falling bombs was small.